When glass fiber insulation or other glass fiber mat products are manufactured, scrap is generated by trimming operations. In many glass fiber manufacturing processes, glass fibers are collected in a loose mat, and treated by application of sizing chemicals and binders which coat the glass fibers to make products or to make them easier to process. After coating, the glass fiber mats are formed into battens or rolls with the edge portions being trimmed off. Generally, the portions trimmed off are disposed of by conventional solid waste disposal procedures. Because of the organic binders and sizing chemicals applied to the glass fiber strands, they cannot be easily remelted and recycled to form glass fibers.
Binders and sizing chemicals are organic compounds comprising primarily carbon, oxygen and hydrogen. If coated glass fiber scrap is introduced into a glass melting furnace, carbon residue from the coating remains after the coating is decomposed.
Carbon residue, even in small amounts, interferes with melting and formation of glass fibers using normal procedures. Another problem associated with recycling glass fiber scrap by melting is the difficulty in causing the glass fiber scrap to blend into a glass melt. Glass fiber scrap has a density of approximately five pounds per cubic foot. The glass fiber scrap tends to float on the surface of the melter, and form a static blanket over the top of a glass melt. Slow heat transfer through the blanket reduces the melting rate of the system in a conventional gas fired glass furnace. Glass fiber scrap fluff floats on top of the melt in conventional glass furnaces and becomes fused on its lower surface by the heat of the melt, and is fused on its upper surface by the temperature of the furnace atmosphere.
Carbon may react with the platinum bushings used to form continuous glass fiber strands or cause other deleterious operational problems in forming insulation products. Carbon also makes the glass black in color which is unacceptable in commercial glass fiber products.
While none of the prior art patents have solved the problems addressed by the Applicant's invention, several patents have addressed aspects of the problem such as the handling of glass fiber fluff. Other patents disclose the use of techniques such as introduction of oxidizing agents to a glass melter.
Three patents which address the problems relating to reprocessing or recycling glass fibers are Grodin U.S. Pat. No. 4,145,202, Propster, et al. U.S. Pat. No. 4,432,780, and Brooks U.S. Pat. No. 4,309,204. The Grodin patent discloses a method for reprocessing glass fibers in a special furnace wherein binders, coatings and sizes are removed. A controlled temperature heating is used to burn off coatings without melting the glass filaments. The glass fiber scrap is ground or milled, and may be added separately or in combination with batch materials. The finely ground scrap may be transported by a pneumatic transporter to either the batch house or the furnace.
The Propster, et al. patent discloses a method of reclaiming chemically coated glass scrap by introducing the scrap into an oxidizing atmosphere of a hydrocarbon fuel fired glass melting furnace. The recycled glass scrap is supplied over the top surface of the furnace with an oxidizing gaseous stream above the glass batch.
The patent to Brooks discloses a processing apparatus for remelting scrap glass fibers wherein a binder is removed in a remelting furnace which is maintained under oxidizing conditions to burn off organic binders or sizes.
Won et al. U.S. Pat. No. 4,545,800, and Kunkle, et al. U.S. Pat. No. 4,632,687 both disclose submerged combustion techniques which occur in a glass melt. In Won, et al., oxygen and hydrogen are combined in a glass melt to form water vapor. The patent to Kunkle, et al. discloses a glass batch process wherein coal is added to a glass batch, and forms a major energy source when combined in the glass batch. After the glass batch is melted, it is further processed in a reoxidization stage. Reoxidization is achieved by introducing oxygen through a bubbler tube and a gas burner.
Several patents have addressed problems of handling glass fiber scrap for recycling including Seng U.S. Pat. No. 4,853,024 and Dunn, et al. U.S. Pat. No. 4,615,720. The Seng patent discloses a scrap recovery apparatus wherein a rotary hot ball mill is used to convert wet scrap fibers into particulate fines. The Dunn, et al. patent discloses a method of controlling the speed at which glass batch is applied to the top surface of a molten glass pool.
These and other problems relating to the technology of recycling glass fiber scrap are addressed by the invention as summarized below.